The reason for poor clinical results or complications seen after laser PWS therapy is the lack of specificity in choosing the optimal light dose to be delivered on an individual patient basis. Presently, all patients are treated with incident doses of laser light based on the subjective clinical judgment of the physician without taking the biophysical, structural, optical and thermal properties of human skin and PWS into consideration. The rationale for using pulsed photothermal radiometry (PPTR) in the clinical management of patients with PWS is that the technique offers a means of documenting the character of a PWS site on an individual patient basis PRIOR to the institution of laser treatment. The epidermal melanin concentration is specified and the initial "T-jump" measurement in response to a subtherapeutic diagnostic laser pulse informs the clinician about the anticipated skin surface temperature elevation in response to a therapeutic laser pulse. Analysis of the magnitude and temporal behavior of the delayed thermal wave provides information on the spatial distribution of heat deposition in the PWS layer as well as its depth. The attending physician who uses PPTR measurements will be in a position to anticipate, and minimize or avoid, epidermal damage while at the same time optimizing destruction of the targeted subcutaneous vessels comprising the PWS. The project will be conducted in the combined basic research laboratories and outpatient clinic at the Beckman Laser Institute and Medical Clinic, University of California, Irvine, and should yield information pertinent to the practical application of the technique to patients. Design and development of the instrumentation will be guided by studies proposed at three levels: (1) in vitro phantom collagen film and model PWS experimentation; (2) in vivo studies on the chicken comb animal model; and (3) clinical trials on PWS patients.